[gn] "port" 8e999e3 (LLVM_ENABLE_IO_SANDBOX)

Author: nico

llvm/utils/gn/secondary/llvm/include/llvm/Config/BUILD.gn

@@ -306,6 +306,7 @@ write_cmake_config("llvm-config") {
     "LLVM_ENABLE_DEBUGLOC_TRACKING_ORIGIN=",
     "LLVM_ENABLE_DUMP=",
     "LLVM_ENABLE_HTTPLIB=",
+    "LLVM_ENABLE_IO_SANDBOX=",
     "LLVM_ENABLE_LLVM_EXPORT_ANNOTATIONS=",
     "LLVM_FORCE_USE_OLD_TOOLCHAIN=",
     "LLVM_HAS_ATOMICS=1",